''I took several snaps with my digital camera and, after downloading them on my computer, noticed one image contained an unidentified object (upper right and trailing the Lancaster) and looking decidedly triangular in shape.

''Nothing was noticed with the naked eye at the time.''

The photographer asked officials for more information.

But the Ministry of Defence desk officer who responded said there were no other reports of UFO sightings that day.

It was not possible to say whether there were military choppers in the area that day without contacting every squadron, the official said.

But he explained it might have been a commercial helicopter from an off-shore oil or gas installation.